As for makeup cosmetics such as a foundation, a feeling in use is considered important, and an ultraviolet shielding property is required in recent years. An ultraviolet shielding material is required to be blended for improving the ultraviolet shielding property. However, zinc oxide microfine particles and titanium oxide microfine particles widely used for a sunscreen agent are inferior in slippage, so that these particles inhibit a good feeling in use. Therefore, an ultraviolet shielding material which can provide an excellent feeing in use has been required.
Further, the zinc oxide particles are used as an inorganic filler contained in a resin composition and a coating. The use of the inorganic filler may include a heat releasing filler utilizing the high thermal conductivity of the zinc oxide particles, a filler for ultraviolet shielding or infrared radiation reflection, and so on.
Furthermore, zinc oxide particles have attracted the attention as inorganic particles having an infrared radiation reflective property, in recent years. The temperature of various products raises when the products absorb infrared radiation. Therefore, for energy saving, a heat insulating coating has been prepared by blending an inorganic pigments which can reflect or shield infrared radiation so that the temperature raising of various products and buildings may be suppressed by using the heat insulating coating.
Zinc oxide particles have an infrared radiation reflective performance. The pattern of absorption wavelength varies depending on the particle shape or particle size. Therefore, if the absorption wavelength in an infrared region is enhanced, an absorption region extends to a visible light region so that a coloring is caused. In the heat insulating coating, the coloring of the pigments for heat insulating is not preferred because the color tone of the obtained coating is influenced.
Patent document 1 discloses hexagonal plate-shaped zinc oxide particles having a controlled particle shape. Hexagonal plate-shaped zinc oxide particles having a particle diameter of 0.5 μm or more are suitably used as particles in foundation applications because very good slippage and excellent feeling in use are provided. However, when the hexagonal plate-shaped zinc oxide particles having an average particle diameter of 0.5 to 1.0 μm disclosed in patent document 1 are used, the slippage is not so bad as the conventional zinc oxide microfine particles but the feeling in use is insufficiently as a material compounded in the current makeup cosmetics. Therefore, it is required to obtain hexagonal plate-shaped zinc oxide particles having a larger particle diameter and a uniform particle size.
Patent Document 2 discloses hexagonal plate-shaped zinc oxide particles having a multilayer structure and having a particle diameter of 10 μm. However, when the zinc oxide particles are compounded in a cosmetic, sufficient good performances in a slippage and so on may not be provided.
Patent Document 3 discloses zinc oxide particles having an average particle diameter of 3 to 20 μm, and an infrared radiation reflective performance and a slippage. However, the particle shape is not disclosed and the obtained particles are indefinite-shaped zinc oxide particles. Such zinc oxide particles cannot exhibit sufficient good performances, for example, the infrared radiation reflective performance and the slippage when used in a cosmetic.